1. Technical Field
Aspects of the present invention relate to an inkjet recording device and an inkjet head which ejects ink onto a recording medium.
2. Description of Related Art
In general, an inkjet printer includes an inkjet head having more than one nozzles from which ink is ejected. In the inkjet head, a meniscus is formed at each tip portion (an ejection orifice) of each nozzle formed on a nozzle surface of a nozzle plate, and then a drop of ink is ejected from each ejection orifice by ink pressure supplied to each nozzle. In order to keep ink ejection performance at a constant level and to thereby keep an appropriate printing quality, the ink pressure is kept at a constant level.
There is a case where ink flowing over an ejection orifice of each nozzle adheres to the nozzle plate or ink bounced off a recording medium adheres to the nozzle plate. If one of such phenomena occurs, ink may accumulate on the nozzle plate and ink pools may appear on the nozzle surface.
If an ink pool caused as above hinders formation of a proper meniscus or an ink pool interferes with the ejection orifice, a steady ink ejection motion can not be kept. That is, there is a possibility that a nozzle becomes unable to eject ink or an ejection direction of ink becomes inappropriate.
As described above, the ink pools cause deterioration of imaging quality. In order to prevent generation of ink pools, one of conventional inkjet printers uses a nozzle plate to which a water repellent agent is applied.
In Japanese Patent Provisional Publication No. HEI 6-344562 (hereafter, referred to as JP HEI6-344562A), a manufacturing process for giving water repellency to a surface of a nozzle plate is disclosed. According to JP HEI6-344562A, a nozzle plate, made of a resin having transparency more than or equal to 10% to an excimer laser having a oscillation wavelength more than or equal to 193 nm, is employed, and a rough surface area in the vicinity of each nozzle on a surface of the nozzle plate is irradiated with the excimer laser in such a manner that the excimer laser does not interfere with a neighboring rough surface area. Consequently, improvement of ejection stability, attainment of wettability, separation of nozzle surfaces can be attained.
An another example of a manufacturing process for giving water repellency to a surface of a nozzle plate is disclosed in Japanese Patent Provisional Publication No. 2000-326514 (hereafter, referred to as JP 2000-326514A). According to JP 2000-326514A, a water repellent film having a thickness smaller than or equal to 0.5 μm is formed on a nozzle plate by subjecting a surface, provided with surface roughness (Ra) of 0.01 to 0.1 by surface roughening, to a process of plasma polymerization (CVD) using a fluorine compound or a silane compound.
In order to keep steady ink ejection performance, one of conventional inkjet printers is configured to periodically perform a wiping operation for wiping remaining ink off a nozzle surface.
As described above, the ink ejection performance can be kept using the above mentioned techniques of conventional inkjet printers. However, the conventional inkjet printer has a drawback that a water repellent layer of a nozzle plate is worn away by the periodically performed wiping operation and therefore the water repellent property deteriorates.
Meanwhile, use of ink having a relatively low surface tension is expected to show better performance of preventing generation of ink pools. However, use of ink having a relatively low surface tension deteriorates wettability and thereby it becomes difficult to uniformly wet the peripheral part of an ejection orifice of each nozzle. In this case, the formation of a proper meniscus and the steady ink ejection performance can not be attained.